Interchangeable lock cylinders, such as, for example, interchangeable core (IC) cylinders, often employ pin tumbler lock mechanisms. Pin tumbler lock mechanisms typically utilize the alignment and misalignment of tumbler pins to control both the operation of an associated lock device and the ability to remove the IC cylinder from a lock housing. For example, with at least certain types of pin tumbler lock mechanisms, in the absence of a valid key being inserted into a key slot of an IC cylinder, tumbler pins typically are biased to be misaligned with, or extend across, both a control shear line and an operating shear line.
When tumbler pins are misaligned with the operating shear line, a plug body of the IC cylinder is typically unable to rotate within the IC cylinder. As the plug body is often operably connected to the lock device, such as, for example, a deadbolt, the inability to rotate the plug body typically results in the inability to displace the lock device from a locked position to an unlocked position, and/or vice versa. Thus, typically in order to lock/unlock the lock device, a first key, such as, for example, an operating key, having the appropriate bitting configuration is placed within a key slot of the plug body. When properly inserted into the key slot, the bittings of the operating key engage and displace tumbler pins to positions in which tumbler pins that are adjacent to the operating shear line, such as, for example, bottom pins, do not extend across the operating shear line while other pins, such as top pins, remain misaligned with the control shear line. With tumbler pins properly aligned with the operating shear line, the plug body may be rotated independently of a control lug of the IC cylinder. Such rotation of the plug body, and associated inability to rotate the control lug, may allow for the displacement of the lock device while prohibiting the removal of the IC cylinder from the lock housing.
Similarly, when tumbler pins, such as top pins, do not extend across the control shear line, the control lug is typically able to rotate within the IC cylinder. The rotational displacement of the control lug is often necessary to displace a retention portion of the control lug from a recess in the lock housing before the IC cylinder may be removed from the lock housing. Thus, the removal of the IC cylinder from the lock housing typically involves the insertion of a second key, such as, for example, a control key, that has an appropriate key bitting configuration to be used in displacing the tumbler pins that are adjacent to the control shear line. Moreover, the bitting of the control key is typically configured so that, when the control key is inserted into the key slot, the top pins are aligned with and/or do not extend across the control shear line. With tumbler pins properly aligned with the control shear line, the control lug may be rotated, which may thereby displace the retention portion so that the IC cylinder may be removed from the lock housing. During such uses of the control key, tumbler pins may continue to be misaligned with the operating shear line, thereby preventing the plug body from being rotated independently of the control lug.
With traditional pin tumbler lock mechanisms, there are a finite number of possible bitting combinations. For example, the possible number of bitting combinations may be defined by the number of bittings in a key system raised to the power of the number of pin chambers in the IC cylinder. For example, if a bitting system uses ten different cuts for the blade of a key, and the IC cylinder has six chambers or collections of tumbler pins, then the number of possible bitting combinations is ten to the sixth power. However, in application, the number of bitting combinations actually used is often less than the number of possible bitting combinations. For example, the number of bitting combinations actually used may be reduced due to manufacturing, mechanical, and/or security concerns, including issues related to reducing the potential for cross keying, phantom master keys, and/or phantom control keys. The number of usable bitting combinations is often further reduced in order to accommodate the ability for each cylinder to have a pin configuration that allows for tumbler pins to align with operating shear line during certain uses and the control shear line during other uses. Additionally, lock mechanisms designed to actuate the control lug off of the position of top pins are generally limited to using traditional tumbler pin systems. Further, the use of different bitting configurations for aligning tumbler pins to both control activation of the lock device and/or removal of the IC cylinder is not necessarily compatible with certain types of interchangeable lock cylinders.